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JEE Main levelSingle correct optionDifficulty 2 of 3o2129

The nitration of benzene-d6 () proceeds at almost the same rate as that of . This shows that

  1. Athe reaction is zero order in benzene
  2. Bthe C-H (C-D) bond is not broken in the rate-determining step
  3. Cthe C-H bond is broken in the rate-determining step
  4. Dthe reaction proceeds through a free-radical chain

Answer: B

A large primary isotope effect would appear only if C-H(D) bond cleavage were rate determining. Equal rates mean the slow step is the attack of forming the arenium ion, and proton loss is fast.
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